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dhcp: Send option 121 if the default gateway is not on the assigned subnet

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This enables CirrOS with udhcpc to set up a route to a gateway
that's not on the assigned subnet, together with:
	https://bugs.launchpad.net/cirros/+bug/1190372

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2021-08-26 14:34:24 +02:00
parent 7eb155ab8f
commit e1c94637ad
1 changed files with 11 additions and 0 deletions
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11
dhcp.c
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@ -308,6 +308,17 @@ int dhcp(struct ctx *c, struct ethhdr *eh, size_t len)
*(unsigned long *)opts[3].s = c->gw4;
*(unsigned long *)opts[54].s = c->gw4;
/* If the gateway is not on the assigned subnet, send an option 121
* (Classless Static Routing) adding a dummy route to it.
*/
if ((c->addr4 & c->mask4) != (c->gw4 & c->mask4)) {
/* a.b.c.d/32:0.0.0.0, 0:a.b.c.d */
opts[121].slen = 14;
opts[121].s[0] = 32;
*(unsigned long *)&opts[121].s[1] = c->gw4;
*(unsigned long *)&opts[121].s[10] = c->gw4;
}
if (c->mtu) {
opts[26].slen = 2;
opts[26].s[0] = c->mtu / 256;